Transmissible spongiform encephalopathies (TSEs or prion disease) are fatal neurodegenerative diseases such as scrapie, Creutzfeldt-Jakob disease (CJD), bovine spongiform encephalopathy and chronic wasting disease (CWD). Our project is aimed at understanding and blocking the conversion of normal PrP (PrP-sen) to PrP-res, the abnormal form of prion protein (PrP) that appears to underlie TSE transmission and pathogenesis. We have employed a wide variety of cell biological, biochemical, biophysical and in vivo experimental approaches. Over the last year we have 1) developed a new high throughput assay for inhibitors of sheep scrapie PrP-res formation, 2) screened several thousand additional compounds for inhibition of PrP-res formation and identified numerous new inhibitors, 3) continued testing of these and other inhibitors for prophylactic and therapeutic activities against scrapie in animals, 4) discovered several new classes of inhibitors of PrP-res formation, some of which dramatically prolong the lives of scrapie-infected animals 5) used confocal microscopy to visualize the pathway by which PrP-res invades neurons and glial cells, initiates infection, and is transported along neuronal processes to extremities where contact is made with other cells, 6) identified and isolated the minimal infectious oligomeric units of PrP-res 7) seeded the formation of amyloid fibrils of full-length recombinant PrP, 8) continued to adapt chronic wasting disease from deer and elk to hamsters and transgenic mice expressing hamster PrP-sen and 9) discovered an antisense probe that can significantly reduce PrP expression in animals.